The present invention relates to a method of manufacturing a heat exchanging fin and a die set for manufacturing the heat exchanging fin.
As shown in FIG. 7, the heat exchanging fin 8, which is employed in a heat exchanger of, for example, an air conditioner, comprises; a plate section 9a made of aluminum, etc.; and collared-through-holes 17 through which heat exchanging tubes (not shown) are pierced.
The heat exchanging fin 8 is formed by a so-called drawing manner. The drawing manner comprising the steps of: drawing a thin aluminum plate to form a plurality of cone-shaped sections; forming the cone-shaped sections into truncated cone-shaped sections, in a plurality of steps, with gradually reducing diameter of the cone-shaped sections; forming through-holes in the truncated cone-shaped sections having prescribed height so as to form into collars 7; and forming flanges 8 at front ends of the collars 7.
The heat exchanging fin 8 formed by the drawing manner is shown in FIGS. 8A and 8B.
Firstly, the cone-shaped sections 1 are formed in a thin plate 9 drawing punches (not shown). Then, the cone-shaped sections 1 are firstly shaped, by first forming punches, into truncated cone-shaped sections 2 with reducing diameter.
The truncated cone-shaped sections 2 are secondly shaped, by second forming punches, into truncated cone-shaped sections 3, whose diameter is shorter than that of the truncated cone-shaped sections 2.
The truncated cone-shaped sections 3 are thirdly shaped, by third forming punches, into truncated cone-shaped sections 4, whose diameter is shorter than that of the truncated cone-shaped sections 3.
The truncated cone-shaped sections 4 have enough height for the collars 7 to be formed.
Further, through-holes 5 are respectively bored, by pierce punches (not shown), in the truncated cone-shaped sections 4, then the collars 7 are formed by burring punches (not shown). Finally, the flanges 8 are formed at the front ends of the collars 7 by flaring means.
In the drawing manner, in which the cone-shaped sections 1 are formed in the thin plate 9 by drawing, parts of the material around the cone-shaped sections 1, which constitute the thin plate 9, are drawn toward the cone-shaped sections 1 while drawing the thin plate 9, so that thickness of the thin plate is not fixed between the cone-shaped sections 1. Therefore, there are formed wrinkles 32 between the adjacent cone-shaped sections 1, and the wrinkles 32 are left after the collared-through-holes 17 are completely formed, so that the heat exchanging fin 8 has a poor appearance.
In the case of forming low collars, dome-shaped sections may be formed, by bulging, in the thin plate instead of forming the cone-shaped sections so as to remove the wrinkles.
In the bulging step, thickness of projected sections, which are formed by punches, are made thinner so as to form the collars. Unlike the drawing manner, in which the parts of the material around the cone-shaped sections are drawn, high collars cannot be formed. But drawing the parts of the material can be reduced, so that the thickness of the thin plate can be fixed between the dome-shaped sections and the wrinkles between the adjacent dome-shaped sections can be reduced.
However, forming the wrinkles 32 cannot be perfectly prevented by bulging. Thus, heat exchanging fins having no wrinkles 32 cannot be manufactured.
A plurality of columns of the collared-through-holes 17, which are arranged in a direction xe2x80x9cBxe2x80x9d in FIG. 8A, are simultaneously formed in the thin plate 9 in one press action of a die set; one or a plurality of rows of the collared-through-holes 17, which are arranged in a direction xe2x80x9cAxe2x80x9d in FIG. 8A, are simultaneously formed in the thin plate 9 in one press action of the die set. Positioning accuracy of the collared-through-holes 17, which are simultaneously formed, depends on manufacturing accuracy of the die set. If the wrinkles 32 are formed between the collared-through-holes 17, they are extended in following steps: a flattening step, a cutting step. By extending the wrinkles 32, pitches between the collared-through-holes 17 are partially changed.
The thin plate 9, in which the collared-through-holes 17 have been formed, is cut to leave the heat exchanging fin 8 including one or a plurality of lines of the collared-through-holes 17 by a cutter blade (not shown). At that time, if there are wrinkles 32 between the collared-through-holes 17, the cutter blade extends the wrinkles 32, so that the pitch of the collared-through-holes 17, between which the wrinkles 32 are formed, is different from the pitch of the collared-through-holes 17, between which no wrinkles 32 are formed.
The fin plate 9 is intermittently sent in the direction xe2x80x9cBxe2x80x9d and cut so as to leave the heat exchanging fin 8. In the cutting step, cutting lines are sometimes partially overlapped. If the wrinkles 32 are formed in the thin plate 9, the wrinkles 32 are extended by the cutting blade, so that the overlapped cutting lines are mutually shifted. By the shift of the cutting lines, flashes are formed in an edge of the heat exchanging fin 8, which corresponds to the overlapped portion.
In each of the steps of shaping the truncated cone-shaped sections, the diameters of the cone-shaped sections or the truncated cone-shaped sections, which have been formed in the prior step, are reduced. If the rate of diameter reduction in each successive step is great, parts of the cone-shaped sections or the truncated cone-shaped sections, which are located outside of the forming dies whose diameter are shorter than that of the cone-shaped sections or the truncated cone-shaped sections to be shaped, are pressed between the forming dies and a lifter when the die set is closed.
The pressed parts are left as circular grooves (ring marks) 30 enclosing the collars 7.
The ring marks 30 are deformed and hardened during the shaping steps, so they cannot be removed in the following steps and adversely influence the shapes of heat exchanging fins 8. The number of the ring marks 30 of each collar 7 is defined by the number of the shaping steps.
An object of the present invention is to provide a method of manufuring a heat exchanging fin, in which forming the wrinkles and the ring marks can be restricted.
Another object of the present invention is to provide a die set for executing the method of the present invention.
In the present invention the method of manufacturing a heat exchanging fin having a plurality of collared-through-holes, comprises the steps of:
forming a plurality of dome sections, whose diameter is greater than inner diameter of the collared-through-holes and which are projected from one side face of a thin plate, and a plurality of circular recesses, whose diameter is greater than that of the dome sections and each of which encloses each of the dome sections and are depressed toward the other face of the thin plate;
forming the dome sections and the recesses into truncated cone-shaped sections having prescribed height in a plurality of steps;
forming a through-hole in each of the truncated cone-shaped sections;
forming edges of the through-holes into collars; and
forming a flange at a front end of each of the collars.
In the method of the present invention, the dome sections and the circular recesses are formed by bulging, so the circular recesses prevent the material constituting the thin plate from being drawn toward the dome sections. With this prevention, no wrinkles are formed between the dome sections, and the thickness of the thin plate can be uniform between the dome sections. Further, the dome sections and the circular recesses are gradually formed into the truncated cone-shaped section in a plurality of steps, so that higher collars can be easily formed.
In the method, the diameter of the dome sections may be nearly equal to that of the truncated cone-shaped sections, which is formed in the first step. In this case, the parts of the cone-shaped sections or the truncated cone-shaped sections, which are located outside of the forming dies whose diameter are shorter than that of the cone-shaped sections or the truncated cone-shaped sections to be shaped, are not pressed between the forming dies and the lifter when the die set is closed, so that no ring marks are formed.
The die set for manufacturing a heat exchanging fin, in which the heat exchanging fin is formed by the steps of forming a plurality of dome sections in a fin plate, forming the dome sections into truncated cone-shaped sections and forming the truncated cone-shaped sections into collared-through-holes, comprises:
a lower die including a bulging punch for forming the dome sections and a lifter being always biased upward by a biasing member and having a through-hole, through which the bulging punch passes when the lifter is moved downward; and
an upper die relatively moving to and away from the lower die, the upper die including a bulging die, which has a die hole accommodating a front end section of the bulging punch when the upper die relatively moved to the lower die,
wherein the bulging die has a projected section, which is projected, from an edge of the die hole, toward the lower die, and
wherein the lifter has a concave section, which encloses the through-hole and which accommodates the projected section and forms a recess section, whose diameter is greater than that of the dome section and which encloses the dome section and is depressed in the opposite direction of the projected direction of the dome section, in the fin plate with the projected section when the upper die relatively moves to the lower die.
In the die set of the present invention, the dome sections and the circular recesses are formed by the bulging die and the bulging punch, so the circular recesses prevent the material constituting the thin plate from being drawn toward the dome sections. With this action, no wrinkles are formed between the dome sections. Further, since the dome sections and the circular recesses are shaped, so that higher collars can be easily formed.
In the die set, a plurality of sets of the bulging punch and the bulging die may be provided for forming the dome sections into the truncated cone-shaped sections in a plurality of steps, and diameter of a forming punch and a forming die of the first step may be nearly equal to that of the bulging punch and the bulging die. With this structure, the parts of the cone-shaped sections or the truncated cone-shaped sections, which are located outside of the forming dies, are not pressed, so that no ring marks are formed.